ASTM_D_6428_-_99.pdf

Designation:D 6428 99Test Method forTotal Sulfur in Liquid Aromatic Hydrocarbons and TheirDerivatives by Oxidative Combustion and ElectrochemicalDetection1This standard is issued under the fixed designation D 6428;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the totalsulfur naturally found in liquid aromatic hydrocarbons,theirderivatives and related chemicals.1.2 This test method is applicable for samples containingsulfur from 0.05 to 100 mgS/kg.1.3 The detector response for this technique within thescope of this test method is linear with sulfur concentration.1.4 The following applies to all specified limits in this testmethod for purposes of determining conformance with this testmethod,an observed value or a calculated value shall berounded off“to the nearest unit”in the last right-hand digitused in expressing the specification limit,in accordance withthe rounding-off method of Practice E 29.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.For specific hazardstatements,see Section 9,and Notes 2-4 and Note 7.2.Referenced Documents2.1 ASTM Standards:D 3437 Practice for Sampling and Handling Liquid CyclicProducts2D 3852 Practice for Sampling and Handling Phenol andCresylic AcidE 29 Practice for Using Significant Digits in Test Data toDetermine Conformance with Specifications32.2Other DocumentsOSHA Regulations,29 CFR,paragraphs 1910.1000 and1910.120043.Terminology3.1 Definitions:3.1.1 oxidative combustion,nprocess in which a sampleunder goes combustion in an oxygen rich environment attemperatures greater than of 650C and compounds decomposeto carbon dioxide,water,and elemental oxides.3.1.2 quartz combustion tube devitrification,nthe sug-gested maximum temperature for a quartz combustion tube is1200C.3.1.2.1 DiscussionSamples containing alkai-metals(ele-ments from the Periodic Group IA(that is,sodium,potassium,etc.)or alkaline earth(elements from the Periodic Group IIA(that is,calcium,magnesium,etc.)will cause quartz todevitrify(that is,become milky white and brittle).4.Summary of Test Method4.1 The sample of liquid aromatic hydrocarbon is injected,at a controlled rate,into a stream of inert gas(helium or argon)or inert gas mixed with oxygen.The sample is vaporized andcarried into a high temperature zone(900C)where oxygen isintroduced.Sulfur compounds,present in the specimen areconverted to sulfur dioxide(SO2).Sulfur dioxide is reactedwith the sensing electrode in a 3-electrode electrochemical cell.This reaction produces a measurable current that is directlyproportional to the amount of sulfur in the original samplematerial.The reaction that occurs is as follows:Combustion:R-S+O2900C+CO2+H2O+SO2+oxidesDetection:SO2+2 H2O electrolyte H2SO4+(2H+)+(2e)5.Significance and Use5.1 Some process catalysts used in petroleum and chemicalrefining may be poisoned when even trace amounts of sulfu-rous materials are contained in the feedstocks.This test methodcan be used to determine total sulfur in process feeds and mayalso be used to control sulfur compounds in finished productswhich fall within the scope of this test method.NOTE1Virtually all sulfur compounds will be detected by thistechnique.1This test method is under the jurisdiction of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.04 on Instrumental Analysis.Current edition approved June 10,1999.Published August 1999.2Annual Book of ASTM Standards,Vol 06.04.3Annual Book of ASTM Standards,Vol 14.02.4Available from the Superintendent of Documents,U.S.Government PrintingOffice,Washington,DC 20402.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.6.Interferences6.1 Moisture produced during the combustion step caninterfere if not removed prior to the detector.7.Apparatus7.1 Pyrolsis Furnacea furnace capable of maintaining atemperature sufficient to volatilize and combust all of thesample and oxidize the sulfur to SO2.The furnace temperaturesfor petroleum substances shall be as recommended by themanufacturer.7.2 Quartz Combustion Tubecapable of withstanding 900to 1200C.The inlet end of the tube holds a septum for syringeentry of the sample and has inlet fittings or side arms for theintroduction of oxygen(O2)and inert gas.The construction issuch that the inert gas(or inert gas and oxygen mixture)sweepsthe inlet zone transporting all of the volatilized sample into ahigh temperature oxidation zone.The oxidation section sh